Just to say you are adding in the breast feeding calories in the wrong place - because that BMR is multiplied to get TDEE, and that's not the case.

But you see that 400 cal estimate for energy expended to make milk?

Here's what to do based on what 2 others have now said worked great - one finished, one is doing it still.

Set MFP to whatever activity level is honest, Lightly Active if at home moving around all day for the baby. If studying really makes it like a 45 hrs desk job/commute weekly without a lot of activity, then select Sedentary.

Set it no Maintenance - no weight loss.

Do NOT account for your breastfeeding in anyway. Your metabolism will be higher to take care of it - and there's your deficit.

Higher here at the start as you feed more often - and have more to lose.
Feed less often later then less deficit, and less to lose at that time.

Log your workouts honestly, and eat those calories back. So if program is 45 min, but 10 min is stretching, than only log 35 min of exercise class workout.
For walking and jogging, get the time down correctly, and the distance actually done. Figure out the pace correctly. If you really did the pace in the description to log it, use it. If you did faster but flat, round down. If you did faster between levels but had hills, round up. The walking and running entries are more accurate than HRM, if honest on the pace.

Weigh your foods that you eat.

Because with thyroid problems, a healthy body reasonable deficit doesn't apply to you, your body's reasonable level is going to be lower.

Because you should not have a big deficit at all, that close to goal weight.
And you won't swap fat for muscle unless you actually do some strength training. Your body has no desire to make muscle that has no use.
And you'd have a hard time looking muscular, wrong hormones, and you'd have to do a perfect workout routine and eat in surplus if you wanted a 1 lb gain of muscle in 6-8 weeks. So nothing to worry about there.
And you can't look tone if you can't see muscle through the fat.